* Bumps any `minSdkVersion`'s below 19 to 19, as the change to only support 19+ has been in stable for a bit now.
* Bumps the minimum required flutter version to 3.16 for the changed packages, as that is the first version in which we started automigrating `minSdkVersion`'s less than 19.
* Also bumps the `minSdkVersion` in the legacy project to `flutter.minSdkVersion`, as this would happen when running an app with `minSdkVersion` < 19.
* Removes some code branches for cases of sdk < 19.
* Fixes some failing tests in `video_player` - for full transparency, I have now idea how these could have been passing before?